Method for charging a fiber suspension, and arrangement for carrying out said method

ABSTRACT

A method of loading a fibrous stock suspension containing chemical pulp fibers with calcium carbonate including the steps of: adding one of calcium oxide and calcium hydroxide in one of a liquid form and a dry form into the fibrous stock suspension; adding gaseous carbon dioxide into the fibrous stock suspension; precipitating of the calcium carbonate through said carbon dioxide; and refining of the fibrous stock suspension during said precipitating step.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to loading of a fibrous stock suspensionwith calcium carbonate.

2. Description of the Related Art

Several methods for loading chemical pulp fibers with calcium carbonateare already known. A method is described in U.S. Pat. No. 6,413,365 B1,where the fibrous material is transported by way of a supply linetogether with calcium oxide and/or calcium hydroxide which are containedin the suspension. From there, the fibrous stock suspension istransported into a rotating distribution device. A reaction gas is fedin a ring shaped pattern into the fibrous stock suspension; this causesthe formation of calcium carbonate crystals in the fibrous suspension.The calcium carbonate crystals are distributed in the fibrous stocksuspension through the rotating distributor device. This process isknown as a Fiber Loading Process.

Additional methods and arrangements for loading fibers in a fibrousstock suspension with a filler or additives are known from German PatentNos. DE 101 07 448 A1 and DE 101 13 998 A1. With the assistance of theseknown processes, cigarette paper, cardboard and all types of packagingpapers, all types of Kraft sack paper and papers containing fillers canbe produced. The following applies to the production of cigarette paper:cigarette paper has a base weight of 16 to 26g/m². It is frequentlyenhanced with an impressed watermark and should be very thin, capable ofglowing combustion, and tasteless. It should also possess good opticalvalues with regard to the brightness. The capability of glowingcombustion is usually achieved by impregnation in order to leave anattractive white ash.

Cigarette paper is normally produced from linen or hemp fibers, cotton,sulfate pulp, paper machine broke, as well as from other fiber sources.The filler content in cigarette paper is between 5% and 40%, whereby 30%is considered as a standard value.

Packaging papers and cardboards can be divided into three categories:Container board for packaging purposes, container board for applicationsin the field of consumer packaging and specialized papers such aswallpaper, book spines, etc. Packaging papers are normally produced asmulti-ply products having basis weights higher than 150 g/m². Thefreeness varies from 600 to 50 CSF or 20 to 80° SR, relative to theproduced end product.

Kraft sack papers require a high porosity and a high mechanical strengthin order to meet the high demands that occur such as rough handlingduring the filling process and the duration of their use, as is thecase, for example, with cement bags. The paper must be strong enough toabsorb impacts and must have an accordingly high energy absorptioncapacity. The sack paper must also be porous and sufficiently airpermeable in order to facilitate effortless filling. Sack papers areproduced, for example, from a long fibered Kraft pulp into producthaving a basis weight of between 70 and 80 g/m², and having a freenessof between 600 to 425 CSF or 20 to 30° SR. In addition, a mediumfreeness, as described above is strived for. This is usually achievedthrough high consistency refining whereas in the case of conventionalpaper grades, for example, graphic papers, low consistency refining isutilized. The result of the high consistency refining is good adhesionof the fibers to each other as well as a high porosity. The sack paperis predominantly produced from bleached and unbleached fibers, whereby afiller content of 5% to 15% may be present in the produced sack paper.

Filter paper requires a high controlled porosity and pore distribution.It must have a sufficiently high mechanical strength to counteract theflow of the medium that is to be filtered. Filter paper is produced,with a basis weight of 12 to 1200 g/m². For example, an air filter would

have a basis weight of between 100 and 200 g/m², an oil and fuel filterbetween 50 and 80 g/m², a foodstuff filter to 1000 g/m², a coffee filterto 100 g/m², a tea bag between 12 and 20 g/m² and a vacuum bag between100 and 150 g/m². All filters are produced from a multitude of fibers,such as chemical pulp fibers, bleached and unbleached fibers, Kraftpulp, DIP (deinked) paper, recycled fibers, TMP (thermo mechanical)paper, etc.

What is needed in the art is a more efficient, less costly method ofloading a fibrous stock suspension.

SUMMARY OF THE INVENTION

The present invention provides a method including the following processsteps:

-   -   Feeding of calcium hydroxide in liquid or dry form, or of        calcium oxide into the fibrous stock suspension,    -   Feeding of gaseous carbon dioxides into the fibrous stock        suspension,    -   Precipitation of calcium carbonate through the carbon dioxide        and    -   Refining of the fibrous stock suspension during the loading        process.

The current invention describes a method for the production of fiberloaded precipitated calcium carbonate (FLPCC) and to simultaneouslyundergo a refining process. The fiber raw material that is to be loadedmay consist of recycling paper, DIP (deinked paper), secondary fibers,bleached or unbleached pulp, mechanical pulp, bleached or unbleachedsulfate pulp, broke, linen, cotton, and/or hemp fibers (predominantlycigarette paper) and/or any paper raw material that can be utilized on apaper machine, irrespective of whether or not the end product contains afiller that was produced by a precipitation process in batch reactors orby a refining process, or whether talcum, titanium dioxide (TiO₂),silicon, etc. are used. The refining process is also referred to as GCCprocess (GCC=ground calcium carbonate).

When a fibrous stock suspension is processed with a fiber loadingtechnology a completely new product for application in paper productionresults. The new product has new and improved characteristics comparedto a product according to the current state of the art. The fiberloading technology permits precipitation of a filler, especially calciumcarbonate, that is uniformly distributed and adhered to, in and betweenthe paper fibers directly in the stock preparation of a paper mill. Italso allows the treated fibrous stock to undergo a fiber treatment in arefiner simultaneously with the precipitation process.

The process for the production of precipitated calcium carbonate withsimultaneous refining with the assistance of the fiber loadingcombination process occurs according to the process data, which isdescribed in further detail below. In this context please also refer toGerman Patents DE 101 07 448 A1, DE 101 13 998 A1 and U.S. Pat. No.6,413,365 B1.

In accordance with the FLPCC combination process described under thepresent invention the filler material utilized according to the currentstate of the art is replaced with the filler material produced accordingto the fiber loading combination process technology. The range ofapplication of the filler produced with the fiber loading combinationprocess technology extends to applications within the paper productionof all paper grades, including cigarette papers, filter papers, Kraftsack paper grades, cardboard and packaging papers that have a fillercontent of between 1% and 60% and/or a white liner having a fillercontent of between 1% and 60%. The loaded and produced paper grades canbe produced on a paper machine from a recycling paper, deinked paper(DIP), secondary fibers, bleached or unbleached pulp, mechanical pulp,bleached or unbleached sulfate pulp, broke, linen, cotton, and/or hempfibers (predominantly for cigarette paper) and/or any paper rawmaterial, irrespective of whether or not the end product contains afiller.

Fibrous stock produced with the fiber loading combination processtechnology generally possesses a superior dewatering characteristic ascompared to a fibrous stock produced according to another method. Theimprovement in the dewatering capacity is between 5 to 100 ml CSF or 0.2to 15° SR, depending upon the required freeness. The stock or pulpproduced according to the fiber loading process further possesses a lowwater retention value of 2 to 25%, depending upon the raw material thatis used in production. This permits a more effective production ofvarious paper grades, for example, FL (FL=fiber loaded) copy andprinting paper of all types, FL coating paper of all types, FL newsprint of all types and FL cigarette paper of all types, FL B&P paper ofall types, FL Kraft sack paper of all types and FL filter paper, sincethe water in the stock suspension can be removed faster. The stocktherefore dries faster.

In the instance of FL cigarette paper, FL B&P paper, FL Kraft sack paperand FL filter paper, which do not require fillers, the exposed fillercan be removed by way of an additionally provided washing process priorto the refining process, following the refining process, after runningthrough the headbox vat or prior to feeding into the paper machine. Thisapplies to the filler that is not deposited in, or on, the fibers andcan be washed out accordingly. The fibers themselves will still containfiller, inside and out so that the positive effects of the fiber loadingtechnology can be taken advantage of.

The fiber loading technology may be utilized, prior to, or after, therefining process, depending on what requirements are put upon the endproduct.

Compared to the current state of the art, a higher freeness value can beachieved with the fiber loading combination technology, since up to 50%of refining energy can be saved. This has an especially positiveinfluence with all the paper grades, which pass through a refiningprocess during their production, or which possess a very high freenessvalue, for example FL-cigarette papers, FL B&P papers, FL Kraft sackpapers and FL filter papers. In particular, these are FL

cigarette papers having 100 to 25 CSF or 68 to 90° SR, FL B&P papershaving 600 to 50 CSF or 20 to 80° SR, FL sack papers having 600 to 425CSF or 20 to 30° SR and FL filter papers having 600 to 350 CSF or 20 to35° SR.

The high mechanical strengths in the end product, which are achievedthrough the high freeness value, positively affect the production of FLcigarette papers, FL B&P papers, FL sack papers and FL filter paperssince, due to process based mechanical loads in the various sections ofthe paper machine. Process based mechanical loads exist in the presssection, the dryer section and in the area where the web is wound, theproduced intermediate product and the end product, which is to beproduced, bears a high mechanical load due to the utilization ofwinders, rewinders and converting machinery. Great mechanical stressesoccur on the paper, especially in the production of cigarette paper,which are also partially attributed to the low basis weight and theutilization of winders.

More effective drying to a residual moisture content of 1 to 20% permitsan increase in efficiency for all paper grades. A higher water retentioncapacity, i.e. 1 to 25% results in a positive influence uponremoistening, which is lower in the manufacturing process, as well asupon the printability of the produced web. An additional advantage forall paper grades is the greater brightness or the higher optical valuesof around 15 or more lightness points, which is to be emphasized in theproduction of all grades of paper and cardboard, with or without a whiteliner. By using the fiber loading technology the optical values, forexample in cigarette papers, are also improved by up to 10 lightnesspoints.

An additional advantage of fiber loading with the above referenced papergrades is found in that for special applications calendering is providedand in doing so the so-called blackening due to deposits of FL particlesin, around, and on, the fibers is suppressed or eliminated through theutilization of the fiber loading process of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawing, wherein:

FIG. 1 schematically illustrates an embodiment of the elements and flowof the method of the present invention.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplification set out hereinillustrate one preferred embodiment of the invention, in one form, andsuch exemplification is not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with one embodiment of the current invention aqueousfibrous stock material, especially aqueous paper stock, having aconsistency of 0.1 to 20%, preferably between 2 and 15% is used asprimary a raw material.

In accordance with the present invention, calcium hydroxide is mixed asthe preferred filler into the aqueous fiber stock material, especiallyinto the paper fiber stock, whereby this has a solids content of between0.01 and 60%. In accordance with the current invention utilization of asource material, other than calcium hydroxide or calcium oxide, for theformation of the filler is also feasible. The calcium hydroxide is addedthrough a static mixer or an intermediate vat. The carbon dioxide ispreferably added into a moist fibrous stock suspension having aconsistency of 0.1 to 15%, according to the reaction parameters. Calciumcarbonate is precipitated in a carbon dioxide gaseous atmosphere.

The refining process is carried out simultaneously with the fiberloading process in an apparatus known as the crystallizer; a refiningenergy in the range of between 0.1 and 300 kWh/ton dry paper pulp isapplied; a short reaction time of the calcium hydroxide and the carbondioxide is important in this context. The energy supply or heat volume,or heating of the paper suspension for the production of crystals invarious forms is important for the present invention.

Depending upon the application of the respective reaction machine,aqueous paper stock with a paper content of between 0.01 and 60% is usedas the primary raw material.

An advantageous embodiment of the method of the present inventionprovides that a refiner, a disperger and/or a fluffer FLPCC reactor areutilized as a reactor and/or a static mixer. The fibrous stock content,especially the paper content used therein is between 0.01 and 15% in theinstance of a static mixer; at between 2 and 40% in the instance of arefiner and a disperger and between 15 and 60% in the instance of afluffer-FLPCC-reactor.

The current invention provides that the dilution water is supplied priorto, during, or after, the addition of carbon dioxide, calcium hydroxideor calcium oxide. Calcium carbonate precipitates when adding carbondioxide into a calcium hydroxide solution or suspension. Conversely, theprecipitative reaction also occurs, when calcium hydroxide is added towater under a carbon dioxide atmosphere. Diluting water may be addedprior to, during, or after, the addition of carbon dioxide or calciumhydroxide. An expenditure of energy of between 0.3 and 8 kWh/t,especially between 0.5 and 4 kWh/t is preferably used for theprecipitation reaction.

Likewise it can be provided that the process temperature is between −15°C. and 120° C., especially between 20° C. and 90° C.

According to the current invention rhombohedral, scalenohedron andspherical crystals can be formed.

Advantageously, the crystals measure between 0.05 and 5 μm, especiallybetween 0.3 and 2.5 μm. Static and/or moving, especially rotating mixingelements, may be utilized. The process is carried out in a pressurerange of between 0 and 15 bar, preferably between 0 and 6 bar. The pHvalue is between 6 and 10, preferably between 6.5 and 9.5. The reactiontime is advantageously between 0.01 minutes and 1 minute, especiallybetween 0.05 seconds and 10 seconds.

The current invention is described in further detail below, citing adesign example and with the assistance of FIG. 1, which illustrates aschematic view of an apparatus for loading of a fibrous stocksuspension. For the purpose of loading a fibrous stock suspension withcalcium carbonate the suspension is transported in a device 1 in a pipeline system that is equipped with control valves 10 and 12. Controlvalve 10 is located in a line 14 through which the piping system isconnected to a static mixer 16. Diluting water can be fed to staticmixer 16 by way of a valve 18. Also, the addition of a suspension ofcalcium hydroxide is controlled by way of an additional valve 22 that isinstalled in a line 20. This is supplied by a preparation apparatus 24,where solid calcium oxide or calcium hydroxide is fed into water. Forthis purpose water is supplied to preparation apparatus 24 by way of aline that is equipped with a valve 26. The suspension produced inpreparation apparatus 24 is passed into line 20 by a pump 28.

The diluted fibrous stock suspension, to which calcium hydroxide wasadded, flows from mixer 16 into line 30 that is equipped with valve 32.From line 32 the suspension is immediately fed into a disperger 42(crystallizer). For the purpose of supplying carbon dioxide, this isconnected with a carbon dioxide tank 52 through a line 50, which isequipped with valves 44 and 46, and a pump 48. Carbon dioxide is fedfrom carbon dioxide tank 52 into disperger 42 in order to produce thedesired precipitation reaction of calcium hydroxide and carbon dioxide

for the formation of calcium carbonate as a filler in the fibers of thefibrous stock. Instead of utilizing a mixer 16, the calcium hydroxidemay also be added from a header tank.

Line 50 is connected by way of an additional valve 58 with a staticmixer 60 whose purpose it is to add additional carbon dioxide to thefibrous stock suspension flowing from disperger 42 through line 64 whichis equipped with valve 62.

Fibrous stock suspension that is not treated with calcium hydroxide canadditionally be fed into blend chest 68 by way of the 12 and line 70.

The fibrous stock suspension flows from static mixer 60 into blend chest68, which is equipped with a rotor 66 for the purpose of thoroughlymixing the fibrous stock suspension. From blend chest 68 the fibrousstock suspension flows either immediately to a headbox in a papermachine, or it is subjected to additional mechanical processing, forexample in a refiner feed chest.

In addition, a refiner 80 can be installed in the piping system for thepurpose of improving the fibrous stock suspension through an additionalrefining process. Refiner 80 is supplied with fibrous stock suspensionby way of a line 82 that branches off of line 30. From refiner 80 therepeatedly refined fibrous stock suspension is brought through line 84into line 64 and from there, as described above, into blend chest 68.

Provisions can additionally be made that carbon dioxide from carbondioxide storage tank 52 is supplied to refiner 80 through line 86 thatbranches off of line 50 and a static mixer 88 that connects line 86 withline 82.

The inventive design of the present invention includes loading of afibrous stock suspension with calcium carbonate that has the advantage,when compared with devices according to the current state of the art, inthat machinery for homogenizing of the fibrous stock suspension, such asa screw press, and a conditioning machine for homogenizing of thefibrous suspension (equalizing reactor) is not required. Refiner 80having a container/vessel additionally takes over the refining process,providing a considerably simpler arrangement of stock preparationcompared to the current state of the art. This refining process servesat the same time as an agitation process, in order to deposit thecalcium carbonate in the fibers through a shear process.

In the inventive method, for preparation of the fibrous stock suspensionby way of the fiber loading process, calcium hydroxide (lime hydrate,lime milk) is used, which has a solubility in water at 20° C. of 1.65g/l to 0.7 g/l at 100° C. A pH value of up to 12.6 is achieved,depending upon how closely the concentration of the solution reaches themaximum value. In commercially available lime hydrate concentrations,solids contents of 0 to 60% can be realized, whereby the suspension hasa pH-value of 12.6 maximum. The actual volume of lime hydrate in thesuspension therefore includes the dissolved component as well as thesolids concentration.

For a suspension containing 20% calcium hydroxide in one liter at 20° C.therefore, a dissolved mass of 1.65 g calcium hydroxide and a solidscontent of 198.35 g results. Since in the fiber loading process theconversion or reaction speed influences the end product of the FL (fiberloading) process every effort is made to use the lime hydrate for an asshort as possible conversion time. This is achieved in that for theproduction of the lime hydrate calcium oxide (CaO), in a medium particlesize range of 0.01 to 100 mm, especially in a size range of 0.05 to 50mm, is produced in a slaking process.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

1-18. (canceled)
 19. A method of loading a fibrous stock suspensioncontaining chemical pulp fibers with calcium carbonate, comprising thesteps of: adding one of calcium oxide and calcium hydroxide in one of aliquid form and a dry form into the fibrous stock suspension; addinggaseous carbon dioxide into the fibrous stock suspension; precipitatingof the calcium carbonate through said carbon dioxide; and refining ofthe fibrous stock suspension during said precipitating step.
 20. Themethod of claim 19, further comprising the step of applying a refiningforce in the range of between approximately 0.1 and 300 kWh per ton ofdry paper pulp, said precipitating step and said refining step areaccomplished in a disperger.
 21. The method of claim 19, furthercomprising the step of providing raw material to the fibrous stocksuspension, said raw material being at least one of aqueous fibrousstock material and aqueous paper stock, said raw material having aconsistency of between approximately 0.1 to 20%.
 22. The method of claim21, wherein said consistency is between approximately 2 to 6%.
 23. Themethod of claim 21, wherein said adding one of calcium oxide and calciumhydroxide step includes the step of mixing said calcium hydroxide intoone of said aqueous fibrous stock material and said aqueous paper stockthereby forming a mixture having a solids content of betweenapproximately 0.01 and 60%.
 24. The method of claim 23, wherein saidmixing step occurs in one of a static mixer and an intermediate vat. 25.The method of claim 19, wherein said adding gaseous carbon dioxideincludes the step of mixing said carbon dioxide into the fibrous stocksuspension that is moist;
 26. The method of claim 19, wherein at leastone of a refiner, a disperger, and a fluffer fiber loaded precipitatedcalcium carbonate (FLPCC) reactor are used as at least one of a reactorand a static mixer.
 27. The method of claim 26, wherein the fibrousstock suspension has one of a fibrous stock content and a paper contentof between approximately 0.01 and 15% while in said static mixer. 28.The method of claim 26, wherein the fibrous stock suspension has one ofa fibrous stock content and a paper content of between approximately 2and 40% while in one of said refiner and said disperger.
 29. The methodof claim 26, wherein the fibrous stock suspension has one of a fibrousstock content and a paper content of between approximately 15 and 60%while in said fluffer-FLPCC-reactor.
 30. The method of claim 19, furthercomprising the step of supplying dilution water one of prior to, duringand after either of said adding steps.
 31. The method of claim 19,wherein energy is expended in the method of between approximately 0.3and 8 kWh/t.
 32. The method of claim 31, wherein said energy is betweenapproximately 0.5 and 4 kWh/t.
 33. The method of claim 19, wherein aprocess temperature is maintained during the method of betweenapproximately −15° C. and 120° C.
 34. The method of claim 33, whereinsaid process temperature is between approximately 20° C. and 90° C. 35.The method of claim 19, wherein the method produces calcium carbonate inat least one of rhombohedral, scalenohedron and spherical crystals. 36.The method of claim 35, wherein said crystals measure betweenapproximately 0.05 and 5 μm.
 37. The method of claim 36, wherein saidcrystals measure between approximately 0.3 and 2.5 μm.
 38. The method ofclaim 19, further comprising the step of using mixing elements that areone of static, moving and rotating.
 39. The method of claim 19, whereina pressure is maintained in the range of approximately 0 to 15 bar. 40.The method of claim 39, wherein said pressure is between approximately 0and 6 bar.
 41. The method of claim 19, wherein a ph is maintained in thefibrous stock suspension of between approximately 6 and
 10. 42. Themethod of claim 41, wherein said ph is between approximately 6.5 and9.5.
 43. The method of claim 19, wherein a reaction time is expended ofbetween approximately 0.01 and 1 minute.
 44. The method of claim 19,wherein a reaction time is expended of between approximately 0.05 and 10seconds.
 45. A fibrous stock suspension loading apparatus, comprising: astatic mixer mixing calcium hydroxide into the fibrous stock suspension;and at least one of a disperger and a refiner for one of fluffing andrefining of the fibrous stock suspension and to precipitate the calciumhydroxide in a carbon dioxide atmosphere while creating fibers that areloaded with calcium carbonate in the fibrous stock suspension.